In the fabrication of semiconductor integrated circuits, most of the manufacturing steps take place in laminar air flow clean rooms which are designed to reduce the number of particles in the production environment. Maintaining this clean room free of particulate matter is critical to the semiconductor integrated circuit fabrication process since the largest single cause of reduced yield is particulate matter.
Wet processing is one of the many steps in semiconductor integrated circuit fabrication. In wet processing, the wafer/substrate is exposed to a variety of liquids, such as acids, bases and solvents, by immersion of the wafer in a tank containing the desired process liquid. Typically, a wet process work station area in a clean room provides a plenum area in which these process liquid tanks and their support plumbing are mounted. It is also desirable to mount the process control electronics immediately adjacent the liquid tanks. In this type of configuration, the wet process work station provides a shell in which to physically mount all of these components. The wet processing work station should additionally provide a controlled environment for processing by containing the liquids and their vapors, as well as controlling and cooperating with the clean room-wide laminar flow past the processing area.
The clean room air flow management in and around a wet processing work station must address the overall laminar flow in the clean room, as well as the localized fume conditions resulting from evaporation of process fluids or workpiece immersion in a particular process fluid. Thus, fume management and air flow control are critical due to the following reasons: safety--proper fume capture prevents exposing the operators to potentially hazardous conditions; process--fume capture prevents any cross-contamination between different chemicals or accidental exposure of the product to unwanted chemical fumes and keeps clean laminar air flowing past the process work area to aid in reducing product defects caused by airborne particulates; environment/facilities--prevention of fumes escaping from within the system reduces potential environmental problems; minimizing the exhaust flow rate required which, in turn, minimizes the makeup air required to replace it, thereby reducing the energy needed and, therefore, the clean room facility operating cost.
There are currently two basic work station designs utilized in the semiconductor industry. The first work station design 10, as shown in FIG. 2 labeled prior art, employs a work surface 12 and flat back 14. In this design, the station 10 must exhaust all of the laminar air flow hitting the deck surface plus an additional small percentage increase to allow for small fluctuations in air velocity while maintaining a positive flow. In the example described with reference to FIG. 2, if the work surface is 30.00 inches wide, then it is estimated that the exhaust rate required per foot of work station length would be 275 to 300 cubic feet per minute (CFM) if the work station were placed in a 100 foot per minute (FPM) laminar area. This exhaust would be directed through the work station area 16 and then through ducts in the wall 18. With some adjustment in exhaust flow rate to balance the system for a specific configuration, this type of station could contain the fumes generated at the work station, and provide a clean laminar air working environment. However, this prior art design requires very high exhaust flow rates resulting in higher clean room operating costs.
The second commonly used work station design 20 for clean room ventilation is shown in FIG. 3, also labeled PRIOR ART. In this apparatus, the horizontal work surface 22 is partially covered by a headcasing 24 and by a shield 26 which extend partially across the width of the horizontal work surface. Like the flat back design described with respect to FIG. 2, the area 28, below the horizontal work surface 22, is hollow and is ducted to exhaust the fumes/vapors through the wall 30. This configuration prevents the laminar flow of air from directly hitting the horizontal work surface. As a result, this flow of air does not have to be exhausted through the work station ducts, and instead is exhausted through the clean room exhaust ducts, placed either in the floor or in the wall baseboards. For purposes of fume control and cleanliness, the important operating principle of this prior art design is to maintain enough air flow through the space between the horizontal work surface 22 and the shield 26 to prevent the escape of fumes from the wet processing work station. The exhaust capacity required to maintain such a positive flow through this front opening can be as low as 100 to 125 CFM per foot of station length, as contrasted with the 275 to 300 CFM per foot required in the flat back design.
Even though this second prior art design permits reduced exhaust air flow rates while maintaining fume containment, it does not adequately maintain a clean working environment because the air flow under head casing 24 and shield 26 is turbulent. There will be one or more air vortices generated under the shield 26 whose axes are parallel to the length of the horizontal work surface. These air flow vortices under shield 26 allow fumes and airborne particles to collect and travel the length of the horizontal work surface 22, which thereby disrupts the clean working environment necessary for semiconductor manufacture.
The present invention provides a ventilated work station design which operates at reduced exhaust flow rates while maintaining laminar flow in the region adjacent the horizontal work surface. This desirable combination of characteristics provides an efficient and simple unit whose operating costs are minimized.
Therefore, it is an object of the present invention to provide a simple ventilated work station design to maintain a laminar flow clean room wet processing work station substantially free of particulate matter.
It is a further object of this invention to provide a ventilated work station in a laminar flow clean room which is safe and which minimizes the risk of operator exposure to potentially hazardous fumes emanating from the ventilated work station wells.
It is a still further object of this invention to provide a ventilated work station for use in laminar flow clean rooms which does not require large (and expensive) exhaust flow capacities through the work station ventilation/exhaust ducts to achieve both fume control and work station cleanliness.
It is another object of the instant invention to provide a ventilated work station, free of turbulent flow regions in the processing area to minimize any potential cross-contamination of substrates due to the uncontrolled migration of fumes from one wet processing well to the next.
These and further objects of the present invention will become readily apparent to those of ordinary skill in the art from the detailed description of the invention and the figures which follow.